Ground Beetle

Common Name: Ground Beetle, Black Ground Beetle, Common Black Ground Beetle – Beetle, as insect, is of Old English origin as bitula from bitan a verb meaning “to bite”. This eventually devolved to bityl in Middle English, with the same pronunciation as the current spelling. Beetle can also mean a heavy wooden mallet in which case it is derived from the Old English bietel, which is derived from the verb “to beat”, as in Beatles [1]

Scientific Name: Pterostichus spp – The genus name is a combination of the Greek words pteron meaning “wing” and stichon meaning “divided by lines”. This refers to the pattern of parallel grooves that extend along the thicken wings called elytra (Greek meaning “sheath”) that cover and protect the dorsal side of beetles. The abbreviated spp signifies species pluralis and is used to refer to a genus and all of its species. There are 150 species of Pterostichus in North America. [2]

Potpourri: While it may seem that there could be nothing more mundane than a common black ground beetle, they are an important capstone species as apex predators of the detritus-covered soil that serves as the font for almost anything that grows. They are ubiquitous, also implied by mundane, which can mean worldly in addition to commonplace. Beetles comprise the order Coleoptera, the largest order in Kingdom Animalia, and make up about a third of all insects. There are some 300,000 species of beetles globally of which about ten percent are indigenous to North America. Coleoptera is a direct Latin translation of the Greek koleooptera meaning “sheathed wings”.  The most distinctive features of beetles are the hard, rigid anterior wings called elytra that are not used for flight but sheath and protect the underlying delicate membranous flight wings. [3] Darwin is frequently credited with the observation that “The Creator would appear as endowed with a passion for stars, on the one hand, and for beetles on the other, for the simple reason that there are nearly 300,000 species of beetle known, and perhaps more, as compared with somewhat less than 9,000 species of birds and a little over 10,000 species of mammals.” The quote is properly attributed to the Neo-Darwinist J. B. S. Haldane. [4]

Beetles are prolific in part because they have carved out unique and surprisingly innovative niches in the tangled web of diverse ecosystems. They come in many shapes and sizes to suit the specifics of their subsistence profile. Tiger beetles are close cousins of ground beetles that chase down their prey at high speed over open ground. Tumblebug scarabs roll up balls of dung as hatcheries and first home for their progeny. Lady bird beetles are divinely benign (called cows of the Virgin Mary in France) for devouring aphids that suck plant fluids and destroy crops. Japanese beetles are an invasive blight to any gardener seeking to specialize in roses or fruit trees. Carrion beetles finish off the carcasses of anything too small or unpalatable to larger predators. Blister beetles exude toxins to protect their eggs from being eaten, named for its effects on the flesh of humans. Ground beetles are the generalists of the lot, living quiet lives under logs, rocks, and wet leaves of the forest. Turn over any log and you are likely to find one or more.

Ground beetles comprise the family Carabidae and are therefore also known as carab beetles or simply carabids. The family name is from the Greek word karabos, originally a type of crab which probably carried over to ground beetles due to the similarity of the hardened outer shell, which serves as an armored shield. Both crab and beetle shells are held together with chitin, an organic polymer that is also the main structural component of most fungi and many algae. Chitin is underappreciated as an important biological compound relative to cellulose, the primary structural component of plant cell walls. Both are polysaccharides, comprised of a string of many (poly) sugars (saccharides). The saccharide of choice for both chitin and cellulose is glucose, better known for its role as animal blood sugar, joined end to end with oxygen bonds. About one half of all carbon that comprises earth’s organic life, sometimes referred to as the biosphere, is cellulose. This amounts to one exagram (10 with 18 zeroes) of carbon that is processed and degraded annually, the mass of a mid-sized asteroid. Chitin differs from cellulose in structure only in having one side-bonded acetyl molecule and is only slightly less abundant as a carbon repository. [5]

Ground beetles also proliferate due to physiological attributes that promote adaptability. The most obvious design feature is the hardened, protective carapace they develop as adults, a property of all beetles. Box turtles live long lives due to the coevolution of a similar structure that wards off all but the most determined assaults. Beetles are attacked by fewer predators than other insects. [6] But there is more to beetles than an “intelligent” design. A study of the response of ground beetles to a combination of abiotic factors such as temperature and humidity and biotic factors such as competition and parasites revealed three distinct advantages: (1) Ground beetles are eurytopic, meaning that they can withstand a wide range of environmental conditions; (2) Ground beetles are adventurous rovers that seek out and colonize new areas; (3) Ground beetles are omnivorous and will consume anything edible. [7] But, as Michael Pollan points out in The Omnivore’s Dilemma, there is some danger in food selections due to toxins and a balance of different nutrients is required. Ground beetle experiments have demonstrated an innate selectivity that accounts for overall nutrition. Beetles fed a pretreatment diet lacking protein subsequently sought out protein-rich foods. A similar behavior was found with lipid or fat nutrient levels.[8]

Of the 3,000 plus carabids in North America, most are voracious predators, both as larvae and as adults. The family Carabidae is in the suborder Adephaga, which literally means glutenous in Greek.  With strong jaws for crushing, they are surprisingly fast and agile. The larvae even have two claws at the end of each of their six legs called urogomfi (literally tail-tooth in Greek) for grasping writhing prey. Ground beetle consumption is prodigious. They can eat over twice their body weight in a single day. In the beetle version of the classic movie Cool Hand Luke in which Paul Newman eats 50 hard-boiled eggs, this would equate to fifty repetitions or 2,500 eggs.  This gustatory act, which would seem to violate the laws of physiology and maybe physics as well is empowered in part by the manner in which food is consumed. Ground beetles regurgitate digestive fluids that partially decompose the crushed carcass to facilitate ingestion as a partially liquified meal, a behavior they share with spiders. And what do they eat? Basically, anything organic that is smaller than they are, which typically consists mainly of invertebrates such as worms, mollusks, and the larvae of other insects (including caterpillars and cockroaches). [9]     

Because of their ubiquity and dining habits, ground beetles are generally good for agriculture, the science (and art) of farming. This is because they consume many things that are bad for agriculture. Crop pests are more frequently remediated with pesticides. Since chemicals that kill tend to be toxic to other living things that cohabit the targeted areas, applying them can also adversely affect the ground beetle population. As a case in point, a field experiment was conducted in Britain to measure the effects of pesticides applied to rid cabbage patches of the maggots (larvae) of the cabbage root fly. The surprising result was that the cabbage fields to which the chemical was applied suffered more maggot damage than those unsprayed as control. Investigation revealed that over 30 species of beetle ate the eggs and larvae of the offending predator and that the pesticide reduced their number to the extent that more root flies survived. [10] Two of the laws proposed by Barry Commoner, the father of ecology, are “Nature knows best,” and “Everything is connected to everything else.” Ground beetles are proof positive, and studies of cultivation practices have been conducted to determine best practices. These have shown that deep tillage depletes ground beetle population whereas reduced tillage with organic fertilization and green manuring promotes them. [11]

Most ground beetles look alike. In fact, the photograph above may very well be a bessbug, a similar beetle that lives in the same rotting log habitat but does not compete with ground beetles since bessbugs consume decaying wood and are not predatory. Even entomologists that specialize in beetles have trouble telling them apart.  The obscure French entomologist René Jeannel (1879 – 1965) spent most of his life studying the speciation of nearly identical cave beetles. After a career of detailed research, he discovered that one of the most reliable identification tools to distinguish one beetle from another was the shape of the male reproductive organ called aedeagus from the Greek aidoia meaning genitals. This practice has continued to the present; it is a relatively common practice for biologists to use both male and female genitalia as a key indicator of species.

Beetle aedeagi generally consist of a capsule-shaped organ from which an inflatable sac extends like a windsock. The extended “penis” is studded with bristles and spines, which must have some purpose as beetles are bisexual and intercourse is de rigueur for procreation. The current hypotheses is that male beetle semen contains chemicals that influence female sexual behavior and that this effect is enhanced by being directly transferred to the blood via spine puncture wounds. Recent experiments employed a micro laser gun to remove some male penal spines to form a test group to compare with a fully-spined control group. The end result was that females impregnated with the fully spined group produced more offspring. The presence of spines on the male sexual appendage is not as outlandish as it sounds. Spines (made of keratin, like hair) are also found on many primates and rodents and there is evidence based on residual DNA that they were they were at some point present on Homo sapiens. [12] So beetles do matter after all.

Footnote: No article on beetles would be complete without reference to the origins of the name of the inimitable Beatles. John, Paul, and George started out as the Quarry Men without a drummer in Liverpool in the late 1950’s. As they gradually developed the sound for which they are so well known today, they decided they needed a more memorable stage name. John is quoted as saying that he was “just thinking about what a good name the Crickets (Buddy Holly’s band) would be for an English group when the idea of beetles came into my head”. He is also credited with changing the spelling to Beatles “to make is look more like beat music, just as a joke”. The original spelling was Beatals.  After a short experiment with Long John and the Silver Beatals, presumably to sound more like Buddy Holly and the Crickets with a literary flourish, Beatals became simply Beatles and the rest is history. [13]

References:

1. Webster’s Third New International Dictionary of the English Language, Unabridged, Merriam Webster Co, Philippines, 1971, p 197.

2. Marshall, S. Insects. Their Natural History and Diversity, Firefly Books, Buffalo New York, 2006, pp 258-259, 287.

3. Milne, L. and M. The National Audubon Society Field Guide to Insects and Spiders, Alfred A. Knopf, New York, 1980, pp 533-621.

4. Haldane, J.B.S. What is life? The Layman’s View of Nature, L. Drummond, London. 1949, p 258 (Verified on paper by Stephen Goranson at Duke University)

5. Voet, D. and J. Biochemistry, John Wiley and Sons, New York, 1990, pp 255-257.

6. Gressitt, J. L. “Coleoptera” Encyclopedia Britannica Micropedia, Volume 4 pp 828-837 William and Helen Benton, publisher, University of Chicago. 1974.

7. Thiele, H. “Carabid Beetles in Their Environments. A Study on Habitat Selection by Adaptations in Physiology and Behavior”. Science August 1978, Volume 201 Issue 4357.

8. Mayntz, D. et al “Nutrient-Specific Foraging in Invertebrate Predators” Science 7 January 2005, Volume 307 Number 5706

9. Goncalves, M. “Relationship Between Time and Beetles in Mata de Cocal” Review of Brazilian Meteorology, Volume 32, Number 4, October 2017.  https://www.scielo.br/j/rbmet/a/kJPLKtB3gLTdfTcMB9vM4Vd/?lang=pt

10. Nardi, J. Life in the Soil, University of Chicago Press, Chicago, Illinois, 2007, pp 136-138

11. Kromp, B. “Carabid beetles in sustainable agriculture: a review on pest control efficacy, cultivation impacts and enhancement” Agriculture, Ecosystems, and Environment, Volume 74, Issues 1-3, June 1999 pp 187-228 https://www.sciencedirect.com/science/article/abs/pii/S0167880999000377?via%3Dihub   

12. Schilthuizen, M. Nature’s Nether Regions, What the Sex Lives of Bugs, Birds, and Beasts Tell Us About Evolution, Biodiversity, and Ourselves. Penguin House, New York, 2014, pp 28-31, and pp 150-157.

13. Spitz, B. The Beatles, Little, Brown and Company, New York, 2005. pp 175, 181, 196.